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Chief petty officer (CPO) is an enlisted naval rank, a type of military rank used by the service organizations of different cultures. As a traditional naval grade, CPO is senior to a petty officer, and is the highest enlisted grade in organizations like Starfleet and the US Navy. In comparison to infantry ranking systems, this rank is approximately equivalent to the more senior sergeant grades. Personnel of this grade can be addressed simply as chief, and sometimes by their job title, such as "chief specialist."

While chiefs are subordinate to all commissioned officers, they have far more experience and practical knowledge than ensigns and lieutenants, and are expected to act as mentors to them and to the junior enlisted assigned. As such, chiefs are often among the actual leaders in a Starfleet organization. Chiefs serve with distinction in most Starfleet branches and specialties, but are particularly visible in engineering and other technical trades.

There are usually individual grades of petty officers, differentiated by first, second class, etc; more senior CPOs are referred to as senior chief petty officer (SCPO) or master chief petty officer (MCPO), referred to as "senior chief" or "master chief" (respectively) in conversation.

In "Mirror, Mirror", Captain Kirk, saved by an enlisted man from Chekov, who intends to assassinate him, is told that "Mr. Chekov was going to make me a chief, sir."

In Star Trek IV: The Voyage Home, a Chief Petty Officer contacts the CDO Commander Rogerson, regarding a power drain in the energy systems of the aircraft carrier Enterprise. The CPO's voice is not heard on screen, but the Commander responds to the question "Yes, Chief. We're tracking that too."